Main Takeaways: This study shows that a congenital amputee used her own representations of sensory information and motor actions to understand other people's body actions when the action was in her repertoire. Instead, if she was not able to perform that action herself (= it was not in her repertoire), different brain areas associated with Theory of Mind (= ability to understand other people's intentions, desires, and beliefs) were also recruited to understand the actions. Similarly, different brain areas were recruited by the congenital amputee for processing other people's pain, based on whether the observed person had body parts that she did not have herself. Therefore, this study highlights how we understand and empathize with people who drastically differ from ourselves.

Title & Authors of the paper: Understanding otherness: the neural bases of action comprehension and pain empathy in a congenital amputee by Lisa Aziz-Zadeh, Tong Sheng, Sook-Lei Liew, Hanna Damasio.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6276973/

Main Takeaways: This study shows that people without limb difference use their mirror neuron system (= activate their own motor-related brain areas when viewing another person's action) when planning to imitate an action performed by either an intact or a prosthetic arm. Prosthesis users were shown to do the same only when planning to imitate an action performed by a prosthetic arm. Instead, when planning to imitate an action performed by an intact arm, they recruited additional brain areas associated with Theory of Mind (= ability to understand other people's intentions, desires, and beliefs). Therefore, this study suggests that prosthesis users use additional brain areas to people without limb difference when planning to imitate a limb not matching their own.

Title & Authors of the paper: Neural activation differences in amputees during imitation of intact versus amputee movements
by William F. Cusack, Michael Cope, Sheryl Nathanson, Nikta Pirouz, Robert Kistenberg, and Lewis A. Wheaton.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3386563/

Main Takeaways: This study uses electroencephalography (EEG), that is a method to record brain activity, to show differences in hand categorization and mental rotation abilities between upper-limb amputees and individuals without limb loss. Specifically, while early-visual processing (= processing of low-level features) was similar between upper-limb amputees and people without limb loss, perceptual salience (= quality of an item by which it stands out from its neighbors) of hand pictures decreased and the intact hand gained more significance in the amputees compared to individuals without limb loss.

Title & Authors of the paper: An event-related potential study on the time course of mental rotation in upper-limb amputees by Yuanyuan Lyu, Xiaoli Guo, Robin Bekrater-Bodmann, Herta Flor, Shanbao Tong.
https://www.sciencedirect.com/science/article/abs/pii/S1388245717300639

Main takeaways: Hand amputees simultaneously watched a (detached) robotic hand prosthesis being brushed, while they felt the brushing of their own (unseen) stump. Synchronous (but not asynchronous) brushing typically gives rise to an illusory sensation of "ownership" over the object (usually a rubber hand) that is being brushed at the same time as one's own hand (this is called the rubber hand illusion). In this study, the felt touch on the stump of amputees was "referred" to the seen touch on the prosthesis, and the prosthesis was then experienced more like a real hand, despite looking robotic. The same feeling that the prosthesis was more real occurred after amputees controlled its movements via muscle recordings from their arm. Contingent multisensory experiences like these could help people to incorporate their prostheses into their body schema even when their look robotic or artificial.

Title and authors of the paper: Referral of sensation to an advanced humanoid robotic hand prosthesis by Birgitta Rosen, H. Henrik Ehrsson, Christian Antfolk, Christian Cipriani, Fredrik Sebelius, and Göran Lundborg. https://www.tandfonline.com/doi/abs/10.3109/02844310903113107